One way to solve this is to not ask customers to trust blindly.
For Webex Teams, the customers can run their own key management server[1]. Traffic gets decrypted using customer-controlled keys running on their own hardware.
For Webex Meetings the media traffic can be encrypted end to end[2]. Of course it breaks all cloud-based features (network recordings, transcriptions, join via web...) but for some users that is the better choice.